1. Field of the Invention
The present invention relates to a denture having the root of an artificial tooth (false tooth) embedded and attached in a plastic denture base (foundation, plate), and to the artificial tooth used in the denture.
2. Description of the Related Art
A denture has the roots of artificial teeth embedded and attached in a denture base made of plastic. The base region of the denture is formed from thermo-setting acrylic resin made up of a mixture including acrylic resin polymer, liquid acrylic resin monomer, and a cross-linking agent. Or, the base region is formed from resins such as thermoplastic polycarbonate resin, polyamide resin, acrylic resin, or polyester resin. Artificial teeth are embedded and attached in the denture base when the base region is formed. Artificial teeth are fabricated from materials such as plastics or ceramics. To embed artificial teeth in the denture base, the roots of the artificial teeth are provisionally held in a plaster mold. In that state, the plaster mold is filled with plastic in a viscous fluid form and thermo-setting plastic is hardened by heating or thermoplastic is hardened by cooling to form the denture. The denture fabricated in this manner has the roots of the artificial teeth embedded and held in the plastic molded denture base.
In a denture of this structure, it is possible for an artificial tooth to separate from (fall out of) the denture base during use. Although an artificial tooth can be made from materials such as plastics, ceramics, or metals, the majority are made of plastic due to its workability, cost, and appearance. Further, the entire artificial tooth or at least the root that embeds in the denture base is commonly fabricated from acrylic resin materials. However, since plastics, including variety of thermoplastics, used to form the denture base region fill the mold in a heated fluid (molten) state and harden by cooling, strong chemical bonding between the artificial tooth and denture base cannot be expected. Particularly such drawback is prominent in case a type of resin material used for the denture base is different from the one of artificial teeth. To resolve this detrimental situation, an artificial tooth has been developed with a through-hole established in the root, and that through-hole is embedded in the denture base region (refer to Japanese Laid-Open Patent Publication 2002-238925).
The denture cited in JP 2002-238925 A is shown in FIG. 1. The denture 11 in this figure has denture base 14 plastic that flows into, and hardens inside the through-hole 13 established in the artificial tooth 12. The plastic that flows into, and hardens inside the through-hole 13 connects with the plastic of the denture base 14 and prevents separation of the artificial tooth 12 from the denture base 14. However, during actual processing to fabricate a denture 11 with this configuration, it is extremely difficult to smoothly flow denture base 14 plastic into the artificial tooth 12 through-hole 13. This is because plastic flows into the through-hole 13 from openings at both ends and air A (FIG. 1 label A) trapped inside cannot escape. As long as air inside the through-hole 13 cannot be discharged, the through-hole 13 cannot be completely filled with plastic. This is because the trapped air blocks the flow of plastic into the through-hole 13. Even if the denture mold if filled with plastic in a pressurized manner, the entire through-hole 13 cannot be filled with plastic if air is trapped inside. This is because the trapped air is compressed but still blocks the flow of plastic. A artificial tooth 12 with a through-hole 13 that is not filled with plastic is not strongly connected to the denture base 14. This is because plastic introduced into the through-hole 13 is cut-off and not continuous through the inside the through-hole 13. When an artificial tooth 12 is embedded in the denture base 14 under these conditions, plastic partially filling the through-hole 13 is easily distorted and the artificial tooth 12 can separate from the denture base 14 when the plastic distorts. Consequently, this configuration has the drawback that even though the artificial tooth 12 is provided with a through-hole 13, it cannot be robustly embedded in the denture base 14 in a manner that keeps the tooth from falling out.
To eliminate this drawback, the present applicant developed the denture shown in FIG. 2. In this denture 21 as well, the root of an artificial tooth 22 is embedded in a molded plastic denture base 24. This artificial tooth 22 is also provided with a through-hole 23a that fills with denture base 24 plastic, and the openings at both ends of the through-hole 23a become buried inside the denture base 24. In addition to establishing the through-hole 23a openings on the surfaces of the artificial tooth 22 that face adjacent teeth on both sides, a vertical hole 23b is established that connects with the through-hole 23a inside the artificial tooth 22. One end of the vertical hole 23b connects with the through-hole 23a, and the other end opens at the bottom-side of the artificial tooth 22. Further, the vertical hole 23b opening is positioned at the bottom-side of the artificial tooth 22 further towards the tip of the root than the through-hole 23a openings. The vertical hole 23b and through-hole 23a fill with the plastic that forms the denture base 24 and robustly hold the root of the artificial tooth 22 embedded in the denture base 24.
The denture 21 described above has an artificial tooth 22 provided with a through-hole 23a having openings in surfaces that face adjacent teeth on both sides, and a vertical hole 23b that connects with the through-hole 23a. One end of the vertical hole 23b connects with the through-hole 23a, the other end opens at the bottom-side of the artificial tooth 22, the vertical hole 23b opening is positioned at the bottom-side further towards the tip of the artificial tooth 22 root than the through-hole 23a openings, and denture base 24 plastic flows into the vertical hole 23b and the through-hole 23a. In particular, the vertical hole 23b of this denture 21 connects with the through-hole 23a and opens below the through-hole 23a further towards the tip of the artificial tooth 22 root than the through-hole 23a. The vertical hole 23b, which has its opening near the bottom of the artificial tooth 22 root, is designed to fill with the viscous fluid plastic of the denture base 24 before the through-hole 23a. In this design, when the vertical hole 23b fills with plastic, plastic does not flow into the through-hole 23a from the through-hole 23a openings. Under these conditions, air is discharged from the through-hole 23a openings by the inflow of plastic from the vertical hole 23b, and the through-hole 23a fills with plastic from the vertical hole 23b. If plastic filling can follow this scenario, air in the vertical hole 23b and through-hole 23a can be smoothly discharged and replaced by denture base 24 plastic. If denture base 24 plastic can fill the vertical hole 23b and through-hole 23a without void formation, the artificial tooth 22 can be solidly connected to the denture base 24 via the plastic and the artificial tooth 22 can be reliably prevented from falling out during use.
See also Japanese Laid-Open Patent Publication 2008-23104
In the denture 21 shown in FIG. 2, the vertical hole 23b and through-hole 23a completely fill with the plastic that forms the denture base 24, and that allows the artificial tooth 22 to be attached in the denture base 24 in a manner that will not fall out. However, to achieve this, plastic must fill the vertical hole before filling the through-hole, and it is necessary for plastic to flow in a manner that discharges vertical hole and through-hole air when it is introduced into the vertical hole. During the fabrication step that forms the denture base, the mold is filled with plastic in viscous fluid form while holding provisionally retained artificial teeth, and precise control of the flow of plastic is difficult. In particular, when plastic is introduced into a plaster mold holding many provisionally retained artificial teeth, it is extremely difficult to introduce plastic initially into the vertical hole of every tooth. If plastic flows in from both the through-hole and the vertical hole of any artificial tooth when the mold is filled with viscous fluid plastic, air residing in the vertical hole or through-hole will not be smoothly discharged. This makes it difficult to attach artificial teeth in the denture base in a manner that will not separate.
The present invention was developed to further resolve the drawbacks described above. Thus, it is an object of the present invention to provide a denture and artificial tooth used in the denture that can solidly attach the artificial tooth in the denture base in a manner that will not fall out without having to precisely control the flow of plastic that forms the denture base.